A flexible display is a display capable of being warped, bent, or rolled without damage through a thin and flexible substrate, like paper. Since a plastic material, a plastic film, or the like is used as the substrate, this flexible display has advantages in that it is light and thin and is not broken even by impact. Therefore, application of the flexible display to a display for a mobile device has been considered. In addition, since the shape of the display may be changed, for example, the display may be bent, in the case in which application of the flexible display spreads to household items, the automotive field, or the like in the future, an explosive demand for the flexible display may be expected, such that a flexible display industry appears promising.
In order to decrease weight of a product, a plastic substrate is used in the flexible displays, but a bending degree is not sufficient or the plastic substrate is vulnerable to scratches, and in the case in which the bending degree is increased, the plastic substrate may be broken. Therefore, in a currently known flexible display, tempered glass or the like has been used as a cover window together with the plastic substrate.
In order to commercialize the flexible display in the true sense, the material of the flexible display should be replaced by a material having sufficient physical properties to replace the tempered glass, or the like. Particularly, in order to commercialize the flexible display in various fields such as for a portable display device and the like, the flexible display should not be broken by pressure or force applied from the outside but should be sufficiently able to be warped and folded.
Therefore, various researches on an external material of a flexible display or a rollable display capable of having high elasticity and protecting a product from being damaged by mechanical, physical, and chemical influence from the outside have been conducted.